Yet another repair for the previouis botched recvfrom() fix; Fix telnet...

Yet another repair for the previouis botched recvfrom() fix; Fix telnet driver: It needs to break out of the read loop if 0 (meaning not conneced) of a value < 0 (an error) is encountered.

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@5541 42af7a65-404d-4744-a932-0658087f49c3